Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $56.94   6.702%   $60.7561   $60.76   $60.75   $60.80  
  Purchase #2 $240.44   10.237%   $265.0538   $265.05   $265.05   $265.10  
  Purchase #3 $200.62   13.620%   $227.9444   $227.94   $227.95   $227.90  
  Purchase #4 $218.90   13.176%   $247.7423   $247.74   $247.75   $247.70  
  Purchase #5 $131.59   3.229%   $135.839   $135.84   $135.85   $135.80  
  Purchase #6 $116.31   11.770%   $129.9997   $130.00   $130.00   $130.00  
  Purchase #7 $248.97   6.464%   $265.0634   $265.06   $265.05   $265.10  
  7 purchase totals = $1,213.77       $1,332.3987   $1,332.39   $1,332.40   $1,332.40